Page 908 - Basic Electrical Engineering

13.4 THERMAL POWER GENERATION FROM FOSSIL FUEL

In a thermal-power-generating station the heat energy from coal, oil or gas is
utilized to produce steam and run steam turbines. The steam turbines are

coupled with generators to produce electrical power output. A coal-based
thermal plant is described in brief in the following section.

13.4.1 Coal-fired Thermal Power Stations

Coal is first powdered, i.e., pulverized and burnt in a furnace and the heat
energy is used to boil water in the boiler to produce steam. The steam from

the boiler is taken to the turbine. The turbine works as a prime mover (drive)
to the generator. Thus, the mechanical energy of the turbine is converted into

electricity. The generated electricity is transmitted to various places through
transmission lines after stepping up the voltage with the help of a

transformer. Here, the chemical energy in coal is first converted to heat
energy, then to mechanical energy, and finally to electrical energy. The

conversion efficiency in a thermal-power-generating station is low due to
heat and other types of losses at various stages of conversion. Fig. 13.1 shows
a schematic representation of a coal-fired power station. As can be seen from

the figure, the steam after passing through the turbine goes to a condenser
where it is condensed into water. This water is again fed to the boiler for

producing steam. The heat from the used steam is taken out and dissipated in
the cooling tower.

In coal-fired stations, the coal is brought from the coal storage area through
the coal conveyer to the coal hopper placed near the boiler. The coal is then

pulverized, i.e., made into powdered form so that complete combustion of
coal takes place in the furnace. The pulverizer may be a rotating drum grinder
or other type of grinders.

Sufficient air is required in the furnace for combustion. Air is drawn from
the atmosphere by the use of a forced draft fan (FD Fan). The FD fan takes

air from the atmosphere and the air is preheated before injecting through air
nozzles on the furnace inside wall. The induced draft fan (ID Fan) assists the
FD fan by drawing out combustible gases from the furnace and maintaining a